Holographic Imaging in Ophthalmology

Introduction

Holography establishes an effective interaction between humans and the digital world. It uses 3D imaging technology and creates new possibilities due to its capability to produce non-contrast high-resolution images and contrast. It was in about 1948 when this holography technology was coined by Dr. Dennis Gabor, for which he even received the Nobel Prize. The word “hologram” means “complete image,” which means reconstructing an image to give complete information about a given part. It refers to an image created when light reflects upon meeting an object, obtained with a dense air-like mist. It is a permanent record of light encapsulated in three-dimensional objects like mirrors and glass. The hologram consists of two beams, a reference and an object beam diverted with the help of a half mirror, followed by converging of the light using two full mirrors.

What Is Holographic Imaging Used In Ophthalmology?

This imaging technique uses a three-dimensional technique to create the images of the eye. It is mainly used in ophthalmology to study the structure of the eye and eye diseases. The current eye imaging techniques cannot provide any resolution better than 1µm (micrometer) with a depth of a few hundred micrometers. Thus, digital holography came into existence, in which the hologram, captured with a digital camera, contains information about the structure over the full depth of the eye. All this information can be reconstructed either optically or numerically. The hologram recording scheme utilizes the working principle of the off-axis digital holographic microscope. The eye lens and cornea form the microscope objective.

What Are the Advantages of Holographic Optical Technique over Conventional Ones?

A hologram is a photographic emulsion having both amplitude and phase. Practically, the process involved and the mathematical principles involved are present everywhere. As the images recorded by the hologram are via a wavefront from the object, the reconstructed images are fully three-dimensional and offer extreme realism. It is quite reasonable to apply holographic techniques to the eyes. It has an enormous capacity for information storage and reconstruction, so holography can be used in ophthalmology.

• A hologram can provide a 3D image of the whole eye or that of several eye parts.

• Focus can be made separately and independently on separate planes of depth.

• There is no need to examine the reconstructed image.

• Focus can be made on different layers of the retina and other tissues.

What Are the Uses of Holography in Clinical Ophthalmology?

It has a huge advantage, especially in clinical ophthalmology, as in ordinary photography, one must determine which portion of the eye must be photographed, like the cornea, iris, anterior and posterior portion of the lens, or the superficial layer of the retina. The portion is then focused and photographed using an instrument like the fundus camera or the photo slit lamp microscope to record it. At a particular time, a photo of a different part of the same eye may be needed, but that may not be available. More precise information can be obtained with holograms even when an ordinary ophthalmic instrument is used, even if there is a change in the intraocular pressure or accommodation. With the special holographic technique, a resolution of about 1 µm can also be obtained. The smallest cone of diameter 0.1 µm can also be visualized.

What Is the Technique of Two-Frequency Holographic Interferometry?

• Two-Frequency Techniques: According to the depth of the object's surface, fringes can be formed for periodic intervals. A contour map can be generated on various parts of the eye, notably the retina, and small changes in height can be detected.

• Double Exposure Interferometry: This allows a displacement between the original and the changed state to be measured. Deformation within the various parts of the eye can be determined using this technique. Not applied to the eyeball due to different experimental conditions. Accompanying changes in the intraocular pressure scleral deformation of the eye are measured.

• Computer Generated Hologram: Can produce an arbitrary wavefront.

What Is the History of Holographic Recording of the Eyes?

Van Lighten et al. first suggested the basic application to the ophthalmic field. The holograms they published were that of the model eye, which uses a lens to form the image hologram. It was stated that the resolution in the reconstructed image could have been better due to the deteriorated state of the wet model eyes. Calkins and Leonard published a recording of the hologram of an eye of the cat. Wiggins had adopted a third technique with a combination of optical fiber coupled with a contact lens.

What Is the Basic Principle of Holography?

The search for three-dimensional realism in photography paved the way for the principle of holograms. The light streaming from the source must itself be photographed. Suppose the light waves, with their amplitude of rapidly moving troughs and crests, can be frozen and photographed in an instant. In that case, the wave can be reconstructed, creating the same three-dimensional character as the object through which the light gets reflected. The holograph exhibits the same function and thus records both the phase and amplitude content of the reflected light wave of a laser beam.

Is Holographic Imaging Safe for Routine Eye Examinations?

Although it is considered safe for routine eye examinations, certain criteria must be followed to ensure safety standards.

• Non-Invasiveness: It avoids physical eye contact, reducing the risk of eye injury and discomfort.

• Low Radiation Exposure: Minimum or no radiation exposure; thus, it is safe.

• Compliance With Standard: The holographic techniques adhere to safety standards, and the regulatory bodies ensure these techniques meet the required standards.

• Expert Oversight: As the experts carry out holography, they ensure proper usage and interpretation of the image.

• Patient Comfort: It is more pleasant than conventional methods.

Conclusion:

It is always a must that the practitioners communicate well with the patients about the procedure and address their concerns. It is a must that informed consent is obtained from the patient’s end, which would ensure better validation of the process. It must be remembered that holographic imaging is a groundbreaking leap in eye care as it offers a three-dimensional perspective that goes beyond the traditional imaging method.